regex match substring unless another substring matches

Question

I\'m trying to dig deeper into regexes and want to match a condition unless some substring is also found in the same string. I know I can use two grepl statem

Answer 1

You can use the anchored look-ahead solution (requiring Perl-style regexp):

grepl("^(?!.*park)(?=.*dog.*man|.*man.*dog)", x, ignore.case=TRUE, perl=T)

Here is an IDEONE demo

• ^ - anchors the pattern at the start of the string
• (?!.*park) - fail the match if park is present
• (?=.*dog.*man|.*man.*dog) - fail the match if man and dog are absent.

Another version (more scalable) with 3 look-aheads:

^(?!.*park)(?=.*dog)(?=.*man)